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        <h2>
          <span class="refentrytitle">butterhp</span>
        </h2>
        <p>butterhp — 
      A high-pass Butterworth filter.
          </p>
      </div>
      <div class="refsect1">
        <a id="idp92571136"></a>
        <h2>Description</h2>
        <p>
      Implementation of second-order high-pass Butterworth filter. This opcode can also be written as <a class="link" href="buthp.html" title="buthp"><em class="citetitle">buthp</em></a>.
    </p>
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      <div class="refsect1">
        <a id="idp92573424"></a>
        <h2>Syntax</h2>
        <pre class="synopsis">ares <span class="command"><strong>butterhp</strong></span> asig, kfreq [, iskip]</pre>
        <pre class="synopsis">ares <span class="command"><strong>butterhp</strong></span> asig, afreq [, iskip]</pre>
      </div>
      <div class="refsect1">
        <a id="idp92637760"></a>
        <h2>Initialization</h2>
        <p>
      <span class="emphasis"><em>iskip</em></span> (optional, default=0) -- Skip initialization if present and non-zero.
    </p>
      </div>
      <div class="refsect1">
        <a id="idp92639552"></a>
        <h2>Performance</h2>
        <p>
      These filters are Butterworth second-order IIR filters. They are slightly slower than the original filters in Csound, but they offer an almost flat passband and very good precision and stopband attenuation.
    </p>
        <p>
      <span class="emphasis"><em>asig</em></span> -- Input signal to be filtered.
    </p>
        <p>
      <span class="emphasis"><em>kfreq</em></span>/<span class="emphasis"><em>afreq</em></span> -- Cutoff or center frequency for each of the filters.
    </p>
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      <div class="refsect1">
        <a id="idp92643536"></a>
        <h2>Examples</h2>
        <p>
      Here is an example of the butterhp opcode. It uses the file <a class="ulink" href="examples/butterhp.csd" target="_top"><em class="citetitle">butterhp.csd</em></a>.

      </p>
        <div class="example">
          <a id="idp92645312"></a>
          <p class="title">
            <strong>Example 96. Example of the butterhp opcode.</strong>
          </p>
          <div class="example-contents">
            <p>See the sections <a class="link" href="UsingRealTime.html" title="Real-Time Audio"><em class="citetitle">Real-time Audio</em></a> and <a class="link" href="CommandFlags.html" title="Csound command line"><em class="citetitle">Command Line Flags</em></a> for more information on using command line flags.</p>
            <pre class="programlisting">
<span class="csdtag">&lt;CsoundSynthesizer&gt;</span>
<span class="csdtag">&lt;CsOptions&gt;</span>
<span class="comment">; Select audio/midi flags here according to platform</span>
-odac     <span class="comment">;;;RT audio out</span>
<span class="comment">;-iadc    ;;;uncomment -iadc if RT audio input is needed too</span>
<span class="comment">; For Non-realtime ouput leave only the line below:</span>
<span class="comment">; -o butterhp.wav -W ;;; for file output any platform</span>
<span class="csdtag">&lt;/CsOptions&gt;</span>
<span class="csdtag">&lt;CsInstruments&gt;</span>

<span class="ohdr">sr</span> <span class="op">=</span> 44100
<span class="ohdr">ksmps</span> <span class="op">=</span> 32
<span class="ohdr">nchnls</span> <span class="op">=</span> 2
<span class="ohdr">0dbfs</span> <span class="op">=</span> 1

<span class="oblock">instr</span> 1	  <span class="comment">; White noise </span>

asig <span class="opc">rand</span> 0.5
<span class="opc">outs</span> asig, asig

<span class="oblock">endin</span>

<span class="oblock">instr</span> 2	<span class="comment">; filtered noise</span>

asig <span class="opc">rand</span> 0.6
ahp  <span class="opc">butterhp</span> asig, 500  <span class="comment">;pass frequencies above 500 Hz</span>
     <span class="opc">outs</span> ahp, ahp

<span class="oblock">endin</span>

<span class="csdtag">&lt;/CsInstruments&gt;</span>
<span class="csdtag">&lt;CsScore&gt;</span>

<span class="stamnt">i</span> 1 0 2
<span class="stamnt">i</span> 2 2.5 2
<span class="stamnt">e</span>

<span class="csdtag">&lt;/CsScore&gt;</span>
<span class="csdtag">&lt;/CsoundSynthesizer&gt;</span>
</pre>
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        <p><br class="example-break" />
    </p>
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      <div class="refsect1">
        <a id="idp92649632"></a>
        <h2>See Also</h2>
        <p>
      <a class="link" href="butterbp.html" title="butterbp"><em class="citetitle">butterbp</em></a>,
      <a class="link" href="butterbr.html" title="butterbr"><em class="citetitle">butterbr</em></a>,
      <a class="link" href="butterlp.html" title="butterlp"><em class="citetitle">butterlp</em></a>
    </p>
      </div>
      <div class="refsect1">
        <a id="idp92653664"></a>
        <h2>Credits</h2>
        <p>
      </p>
        <table border="0" summary="Simple list" class="simplelist">
          <tr>
            <td>Author: Paris Smaragdis</td>
          </tr>
          <tr>
            <td>MIT, Cambridge</td>
          </tr>
          <tr>
            <td>1995</td>
          </tr>
        </table>
        <p>
    </p>
        <p>Existed in 3.30</p>
        <p>Audio rate parameters introduced in version 6.02</p>
        <p>October 2013.</p>
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